Cardiac arrhythmias, the most common of which is ventricular tachycardia (VT), are a leading cause of death. In a majority of patients, VT originates from a 1 mm to 2 mm lesion located close to the inner surface of the heart chamber. One of the treatments for VT comprises mapping the electrical pathways of the heart to locate the lesion followed by ablation of the active site.
Commonly assigned U.S. Pat. No. 5,546,951; U.S. patent application Ser. No. 08/793,371; and PCT application WO 96/05768, which are incorporated herein in their entirety by reference, disclose methods for sensing an electrical property of heart tissue, for example, local activation time, as a function of the precise location within the heart. The data are acquired with one or more catheters that are advanced into the heart using catheters that have electrical and location sensors in their distal tips. Methods of creating a map of the electrical activity of the heart based on these data are disclosed in commonly assigned U.S. patent application Ser. Nos. 09/122,137 and 09/357,559 filed on Jul. 24, 1998 and Jul. 22, 1999, respectively, which are also incorporated herein in their entirety by reference. As indicated in these applications, location and electrical activity is preferably initially measured on about 10 to about 20 points on the interior surface of the heart. These data points are then generally sufficient to generate a preliminary reconstruction or map of the cardiac surface to a satisfactory quality. The preliminary map is often combined with data taken at additional points in order to generate a more comprehensive map of the heart's electrical activity. In clinical settings, it is not uncommon to accumulate data at 100 or more sites to generate a detailed, comprehensive map of heart chamber electrical activity. The generated detailed map may then serve as the basis for deciding on a therapeutic course of action, for example, tissue ablation, to alter the propagation of the heart's electrical activity and to restore normal heart rhythm.
Catheters containing position sensors may be used to determine the trajectory of points on the cardiac surface. These trajectories may be used to infer motion characteristics such as the contractility of the tissue. As disclosed in U.S. Pat. No. 5,738,096 which is incorporated herein in its entirety by reference, maps depicting such motion characteristics may be constructed when the trajectory information is sampled at a sufficient number of points in the heart.
Electrical activity at a point in the heart is typically measured by advancing a catheter containing an electrical sensor at or near its distal tip to that point in the heart, contacting the tissue with the sensor and acquiring data at that point. One drawback with mapping a cardiac chamber using a catheter containing only a single, distal tip electrode is the long period of time required to accumulate data on a point-by-point basis over the requisite number of points required for a detailed map of the chamber as a whole. Accordingly, multiple-electrode catheters have been developed to simultaneously measure electrical activity at multiple points in the heart chamber.
U.S. Pat. No. 5,487,391, directed to systems and methods for deriving and displaying the propagation velocities of electrical events in the heart, is illustrative of contact methods found in the art. In the system disclosed in the '391 patent, the electrical probe is a three-dimensional structure that takes the form of a basket. In the illustrated embodiment, the basket is composed of 8 spines, each of which carries eight electrodes, for a total of 64 electrodes in the probe. The basket structure is designed such that when deployed, its electrodes are held in intimate contact against the endocardial surface.
U.S. Pat. No. 5,848,972 to Triedman et al. discloses a method for endocardial activation mapping using a multi-electrode catheter. In the method of the '972 patent, a multi-electrode catheter, preferably, a 50-electrode Webster-Jenkins™ basket catheter from Cordis-Webster of Baldwin Park, Calif., is advanced into a chamber of the heart. Anteroposterior (AP) and lateral fluorograms are obtained to establish the position and orientation of each of the electrodes. Electrograms are recorded from each of the electrodes in contact with the cardiac surface relative to a temporal reference such as the onset of the P-wave in sinus rhythm from a body surface ECG.
U.S. Pat. No. 5,297,549 to Beatty et al. (the “Beatty method”), the disclosure of which is incorporated herein by reference, discloses a method and apparatus for mapping the electrical potential distribution of a heart chamber. In the Beatty method, an intra-cardiac multielectrode mapping catheter assembly is inserted into the heart. The mapping catheter assembly includes a multi-electrode assembly with an integral reference electrode, or, preferably, a companion reference catheter. In use, the electrodes are deployed in the form of a substantially spherical assembly. The electrode assembly is spatially referenced to a point on the endocardial surface by the reference electrode or by the reference catheter which is brought into contact with the endocardial surface. The preferred electrode assembly catheter is said to carry at least 24 individual electrode sites. Additionally, the Beatty method requires knowledge of the location of each of the electrode sites on the assembly, as well as a knowledge of the cardiac geometry. These locations are preferably determined by the method of impedance plethysmography.
U.S. Pat. No. 5,311,866 to Kagan et al. discloses a heart mapping catheter assembly including an electrode assembly defining a number of electrode sites. The mapping catheter assembly also comprises a lumen to accept a reference catheter having a distal tip electrode assembly which may be used to probe the heart wall. In the preferred construction, the mapping catheter comprises a braid of insulated wires, preferably having 24 to 64 wires in the braid, each of which are used to form electrode sites. The catheter is said to be readily positionable in a heart to be used to acquire electrical activity information from a first set of non-contact electrode sites and/or a second set of in-contact electrode sites.
U.S. Pat. Nos. 5,385,146 and 5,450,846 to Goldreyer disclose a catheter that is said to be useful for mapping electrophysiological activity within the heart. The catheter body has a distal tip which is adapted for delivery of a stimulating pulse for pacing the heart or an ablative electrode for ablating tissue in contact with the tip. The catheter further comprises at least one pair of orthogonal electrodes to generate a difference signal indicative of the local cardiac electrical activity adjacent the orthogonal electrodes.
U.S. Pat. No. 5,662,108 to Budd et al. discloses a process for measuring electrophysiologic data in a heart chamber. The method involves, in part, positioning a set of active and passive electrodes into the heart; supplying current to the active electrodes, thereby generating an electric field in the heart chamber; and measuring said electric field at said passive electrode sites. In one of the disclosed embodiments, the passive electrodes are contained in an assembly positioned on an inflatable balloon of a balloon catheter. In preferred embodiments, the assembly is said to have from 60 to 64 electrodes.
Recent common practice is to use a quadrapolar catheter to map the various chambers of the heart. Moreover, a catheter is dragged around the entire chamber until enough points can together be extrapolated to provide enough information.
Thus, various methods have been proposed for increasing the speed of acquiring an electrical map of the heart. However, there remains a desire for a mapping catheter that reduces procedure time, by providing a distal electrode assembly that can expand and capture a heart chamber structure with a single sweeping moment. For example, with a slight rotation or translating motion, the assembly should be able to contact enough of the heart wall to be able to construct a complete map of the chamber. The assembly should be of a suitable shape, size and flexibility to avoid “tenting” of the heart tissue while being able to follow the motion of heart contractions.